'use strict';

const preserveCamelCase = string => {
  let isLastCharLower = false;
  let isLastCharUpper = false;
  let isLastLastCharUpper = false;

  for (let i = 0; i < string.length; i++) {
    const character = string[i];

    if (isLastCharLower && /[a-zA-Z]/.test(character) && character.toUpperCase() === character) {
      string = string.slice(0, i) + '-' + string.slice(i);
      isLastCharLower = false;
      isLastLastCharUpper = isLastCharUpper;
      isLastCharUpper = true;
      i++;
    } else if (isLastCharUpper && isLastLastCharUpper && /[a-zA-Z]/.test(character) && character.toLowerCase() === character) {
      string = string.slice(0, i - 1) + '-' + string.slice(i - 1);
      isLastLastCharUpper = isLastCharUpper;
      isLastCharUpper = false;
      isLastCharLower = true;
    } else {
      isLastCharLower = character.toLowerCase() === character && character.toUpperCase() !== character;
      isLastLastCharUpper = isLastCharUpper;
      isLastCharUpper = character.toUpperCase() === character && character.toLowerCase() !== character;
    }
  }

  return string;
};

const camelCase = (input, options) => {
  if (!(typeof input === 'string' || Array.isArray(input))) {
    throw new TypeError('Expected the input to be `string | string[]`');
  }

  options = Object.assign({
    pascalCase: false
  }, options);

  const postProcess = x => options.pascalCase ? x.charAt(0).toUpperCase() + x.slice(1) : x;

  if (Array.isArray(input)) {
    input = input.map(x => x.trim())
      .filter(x => x.length)
      .join('-');
  } else {
    input = input.trim();
  }

  if (input.length === 0) {
    return '';
  }

  if (input.length === 1) {
    return options.pascalCase ? input.toUpperCase() : input.toLowerCase();
  }

  const hasUpperCase = input !== input.toLowerCase();

  if (hasUpperCase) {
    input = preserveCamelCase(input);
  }

  input = input
    .replace(/^[_.\- ]+/, '')
    .toLowerCase()
    .replace(/[_.\- ]+(\w|$)/g, (_, p1) => p1.toUpperCase())
    .replace(/\d+(\w|$)/g, m => m.toUpperCase());

  return postProcess(input);
};

module.exports = camelCase;
// TODO: Remove this for the next major release
module.exports.default = camelCase;
